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Outlook fix · classic Outlook (Windows)

Fix Outlook that's not responding or frozen

If classic Outlook keeps showing "(Not Responding)", freezes or hangs, it's usually a temporary indexing or send/receive that clears on its own - or a stuck add-in, a graphics glitch, or a bloated data file. Work through the safe, ordered steps below, or we'll connect and unfreeze it for you remotely today. Rated 4.9 on Google.

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By the 365 Techies team · Reviewed 18 October 2026

First, don't panic

Why Outlook says (Not Responding)

Seeing (Not Responding) in the title bar rarely means anything is broken. Often Outlook is simply busy - indexing a large mailbox, running a big send/receive, or waiting on a slow server - and it comes back to life on its own after a minute or two. It's worth giving it a moment before you do anything drastic.

If it's genuinely stuck and won't recover, the usual culprits on classic Outlook for Windows are a misbehaving add-in, a graphics-rendering glitch, a damaged Office install, or a very large or fragmented data file that Outlook has to wade through. The steps below work through these in the right order. None of them delete your email - your mail stays safe on the server (Microsoft 365, Exchange, IMAP or Google Workspace) throughout, and we flag the one step that touches a local file.

// WINDOWS PCS ONLY

We do not support Outlook on Apple Macs, iPads or iPhones. Apple does not allow our remote-support tool to take control of an iPad or iPhone (an Apple restriction), and our remote support covers Windows PCs only. On an Apple device, Microsoft’s own Outlook help is the place to start.

// FIX IT WITH ME · STEP BY STEP

Fix it with me, one step at a time

The steps from this guide, one at a time, in the order that fixes the most cases fastest. Tell it what happened and it shows the next step. Nothing here leaves your device.Last reviewed 18 October 2026

Checking which Windows you have…STEP 1 OF 6
  1. 01Give it a minute, then force-close if needed

    A large mailbox indexing or a big send/receive can freeze Outlook temporarily - wait a minute or two. If it's still stuck, press Ctrl+Shift+Esc, select Outlook and click End task, then reopen it.

    Is it working now?

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The fix

How to fix Outlook that's not responding

For classic Outlook for Windows, in order. The first three steps often solve it.

  1. Give it a minute, then force it closed if needed. A large mailbox indexing or a big send/receive can freeze Outlook temporarily - wait a minute or two and it often recovers. If it's still truly stuck, close it firmly: press Ctrl+Shift+Esc to open Task Manager, find Outlook in the list, select it and click End task, then reopen Outlook.
  2. Start in safe mode and check your add-ins. Press Windows key + R, type outlook /safe and press Enter to start Outlook with add-ins disabled. If it's stable in safe mode, an add-in is the cause: close it, reopen normally, go to File > Options > Add-ins, set Manage: COM Add-ins at the bottom and click Go, then untick all the add-ins. Re-enable them one at a time (restarting Outlook between each) until the freeze returns - that's your problem add-in.
  3. Turn off hardware graphics acceleration. On builds that still have it, go to File > Options > Advanced > Display and tick Disable hardware graphics acceleration, then restart Outlook. On current Microsoft 365 builds that tickbox may be missing - in that case it's a registry setting your IT team (or us) can apply for you, or you can update your graphics driver instead.
  4. Repair Office. Go to Settings > Apps (right-click Start > Installed apps), find Microsoft 365 / Office, choose Modify and run Quick Repair first (fast, offline, doesn't touch your mail). If it's still freezing, run Online Repair - it's more thorough and needs an internet connection.
  5. Trim a large or fragmented data file. A PST or OST that has grown to tens of gigabytes makes Outlook sluggish and prone to hanging. Archive old mail, empty Deleted Items and Junk, and (on Exchange/365) reduce the offline mail slider under File > Account Settings > Change. Compacting the data file also helps.
  6. Check your antivirus isn't scanning the mailbox live. Some security software scans the .pst/.ost file in real time, which locks Outlook up. Add your Outlook data file (and Outlook itself) to your antivirus exclusions, or temporarily disable its email/file scanning to test.
  7. Create a new mail profile as a last resort. If nothing above helps, a corrupt profile can cause repeated hangs. Go to Control Panel > Mail > Show Profiles > Add, create a fresh profile and re-add your account. Server mail re-downloads automatically - back up any local-only PST first so nothing on your PC is lost.

Keeping your data safe

Is any of this risky for my emails?

Almost none of it. Force-closing Outlook, safe mode, disabling add-ins, turning off graphics acceleration and repairing Office don't touch your mail at all - your emails live on the server and simply re-sync. Quick Repair and Online Repair fix the Office program, not your mailbox.

The one step to be careful with is trimming or compacting the data file, or rebuilding your profile, and only if you have a local-only PST archive that exists solely on your PC (not mirrored on the server). Before archiving, compacting or rebuilding a profile, copy that PST somewhere safe first. If you're not sure whether your data is on the server or only on your PC, don't guess - that's exactly the kind of thing we'll confirm for you remotely so nothing is lost.

// KEEP GOING

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// GOOD QUESTIONS

Frequently asked

Does (Not Responding) mean Outlook has crashed?

Usually not. It often means Outlook is busy - indexing a large mailbox, running a big send/receive, or waiting on a slow server - and it typically recovers on its own after a minute or two. Give it a moment before force-closing it.

How do I force Outlook to close when it's frozen?

Press Ctrl+Shift+Esc to open Task Manager, find Outlook in the list, select it and click End task. Then reopen Outlook. This is safe - your emails are stored on the server, not in the running program.

How do I start Outlook in safe mode to test add-ins?

Press Windows key + R, type outlook /safe and press Enter. That starts Outlook with all add-ins disabled. If it stops freezing, an add-in is the cause - disable them under File > Options > Add-ins (Manage: COM Add-ins > Go) and re-enable them one at a time to find the culprit.

Where is the 'disable hardware graphics acceleration' option?

On builds that still have it, it's under File > Options > Advanced > Display. On some current Microsoft 365 builds that tickbox has been removed, in which case it's a registry setting your IT team or we can apply for you - or you can update your graphics driver instead.

Can 365 Techies fix a frozen Outlook remotely?

Yes. Via Splashtop SOS we phone first, you click one link and watch the whole session, and access ends the moment we're done. We'll find what's making Outlook hang - an add-in, a graphics glitch, a bloated data file - and get it responding again, usually within minutes. Windows and Android only. Call 01202 775566.

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